The present application relates to extracorporeal shock wave technology and in particular, an electromagnetic, electrohydraulic or piezoelectric shock wave device that propagates planar waves, and to methods of using such a device, for developing shock waves and for treating tissue.
Shock waves are used in different medical disciplines and in different species. Although it is not known exactly how specific tissue responds to the shock wave, it is proven that shock waves can have a therapeutic effect and improve certain medical conditions.
In urology, the shock wave is used to disintegrate kidney or urethra stones. In orthopedics, shock waves are used to stimulate bone growth in non-unions. Shock wave therapy is further used to treat epicondylitis, tendonitis calcarea of the shoulder, achillodynia calcaneal spurs, and many other conditions. Shock waves are also used in veterinary medicine to treat ligaments, tendons, splint bone fractures, navicular syndrome, back pain, and certain joint conditions.
Commercially available devices use either high-energy focused shock wave systems or radial emitting pressure pulse systems. In these systems the shock wave is generated either by an electrical discharge in a liquid (electro hydraulic), electrical discharge in an electrical coil that drives a diaphragm (electro magnetic), electrical discharge in piezo elements (piezo electric) or a projectile that hits its target (ballistic system).
Focused shock wave systems have an advantage over radial systems because the shock wave reaches its maximal density inside the body. This allows for the treatment of deeper tissue inside the body. Typical penetration depths in orthopedic devices are 100 mm in human medicine or up to 80 mm in veterinary medicine.
Radial systems can only treat superficial conditions because the diverging wave loses energy density with the square of the distance to the source, leading to insufficient energy density to show an effect on deeper tissue inside the body.
Investigations have shown that, for a tissue to respond, the shock wave must reach a certain energy density measured in mJ/mm.sup.2 (milli Joules per square millimeter).
Also the volume of the treated tissue (or area for rather two-dimensional treatment regions, such as tendons) plays an important factor. Treatment results show that these two factors have the major influence on the clinical outcome.
Focused systems have enough energy density in deeper regions but the treatment area is often too small. Either the shock wave source or the patient must be moved to treat a bigger area.
Radial systems treat a bigger area, but the power density is too small to show an effect in deeper tissues.
Electro-hydraulic shock wave systems have been used to disintegrate kidney and urethral stones by applying focused shock waves to the stone. A few hundred up to a few thousand shock waves may be required to break a stone within a mammal into small pieces of 3-4 mm diameter which are able to pass over a period of several weeks through the urethra and the bladder out of the patient's body.
Devices using electro-hydraulic (U.S. Pat. No. 4,539,989), piezoceramic (U.S. Pat. No. 5,119,801) or electromagnetic (U.S. Pat. No. 5,174,280) shock wave or pressure pulse generating elements have been described.
The patents used herein to illustrate the invention and, in particular, to provide additional details respecting the practice are incorporated herein by reference in their entirety.
In certain of non-urological applications, shock waves and pressure pulses may be used to treat/cure orthopedic painful conditions. The treated indications may be related to tendons, ligaments, soft tissue and include muscle pain and calcification in tissue. Suitable devices and procedures have been described (U.S. Pat. Nos. 5,545,124 and 5,595,178). The treatment of tissue with shock waves has also been discussed (United States Patent Application 20040162508).
In certain non-urological applications, shock waves are used to treat ischemic heart tissue for generating better blood supply in the treated tissue and thus recover the tissue's functionality.
Known devices generally make use of more or less strong focused shock waves which are focused by ellipsoidal reflectors in electro-hydraulic devices (U.S. Pat. No. 4,539,989) or by parabolic reflectors in devices using electromagnetic sources which are emitting waves from a cylindrical surface (U.S. Pat. No. 5,174,280). Other electromagnetic sources may make use of acoustic lenses of different shapes, for example, concave or convex, depending on the sound velocity and density of the lens material used (U.S. Pat. No. 5,419,335 and European Patent 1 445 758 A2). Piezoelectric sources often use spherical surfaces to emit acoustic pressure waves which are self focused to the center of the sphere (U.S. Pat. No. 5,222,484). The same type of focusing has been used in spherical electromagnetic devices (U.S. Pat. No. 4,807,627).
There is a need for an apparatus and a process for optimized electro-hydraulic pressure pulse generation by changing the focusing characteristics of a pressure pulse or shock wave so that unfocused wave fronts with plane or nearly plane acoustic wave front and/or convergent off target or divergent acoustic wave front characteristics can be released by the apparatus. As used herein, convergent off target is where the focal region or point is moved away from the treated tissue.
There is also a need for an apparatus for optimized pressure pulse/shock wave generation, wherein waves with defined wave front characteristics, like focused and/or plane, nearly plane, convergent off target and/or divergent are released from the apparatus for treating tissues, in particular, for treating soft tissue, skin or skin near conditions including, but not limited to, skin and skin near conditions caused by trauma or diseases.
There is also a need for providing an apparatus that allows treatment without requiring extensive scanning of the area to be treated. This is usually required to cover an area uniformly if apparatuses using a small focal point are used. Such an apparatus would reduce treatment times.
There is a need for an apparatus that produces waves having plane, nearly plane, convergent off target or divergent acoustic wave front characteristics with adjustably reducible or reduced energy densities compared to wave fronts emitted by focused shock wave generators.
There is also a need for an apparatus and method that allows using existing pressure pulse generating devices to treat tissues which have more area like than volume like characteristics, such as skin.
The task of the present invention is to optimize the interaction of the shock wave with the tissue of a subject being treated so as to achieve the best clinical result. This task is accomplished by using high-energy shock waves that are generated by electro hydraulic, electro magnetic, or piezoelectric means, but not focused into a focal point. Instead, the shock wave is reflected or refracted in such a way that a “plane wave” or “flat wave” is emitted from the source.
With a “plane” or “flat” wave, the energy is neither converging (as with the focused shock wave) or diverging (as with a radial wave). Rather the energy distribution over the emitting area stays the same even in different distances along the axis of the shock wave source. The initial shock wave energy must be enough to reach a certain energy density at the distal end of the shock wave source.